1. Field of the Invention
This invention relates to a method of removing a contaminant from contaminated material. More specifically, it relates to a method of removing a contaminant, such as arsenic, from spent contaminant-removing material that has been used to remove the arsenic from a synthetic crude or the like.
2. Description of the Prior Art
Only recently, it has been discovered by co-workers Gary Myers and Donald Wunderlich that solid particulate material can be employed to remove a contaminant, such as selenium or arsenic, from a fluid in order to avoid poisoning downstream catalyst employed in further treating the fluid; for example, to prevent poisoning of an expensive hydrogenation catalyst. The particulate material and method are defined in patent application Ser. No. 314,015, filed Dec. 11, 1972, now abandoned in favor of Ser. No. 421,139, filed Dec. 3, 1973 by inventors Gary A. Myers and Donald K. Wunderlich, entitled "Synthetic Oil Treatment" and assigned to the assignee of this application. The descriptive matter of that patent application is incorporated herein by reference for the details needed for full and complete understanding of this invention.
Specifically, patent application Ser. No. 314,015 recited at page 2 et seq: "It has now been discovered that at least one of antimony, arsenic, selenium, and phosphorus can be removed from a hydrocarbonaceous liquid which is not naturally occurring, (i.e., is not a naturally occurring crude oil or a fraction derived therefrom) but which is obtained from normally solid coal, oil shale, or tar sands. Th hydrocarbonaceous liquid of this invention can, therefore, be a synthetic crude oil or a fraction derived therefrom. The non-naturally occurring hydrocarbonaceous liquid is contacted with a material selected from the group consisting of iron, cobalt, nickel, oxides of one or more of those metals, sulfides of one or more of those metals, and combinations of two or more of said metals, oxides, and/or sulfides. The sulfide form is presently preferred.
"The above materials are employed on the synthetic oil (this includes synthetic crude oil or a fraction thereof) under a reducing atmosphere and at an elevated temperature of at least 300.degree. F., there being substantially no water present. In this manner, the impurities are taken up by the material itself in a substantially water insoluble form.
"In th discussion of this invention, reference to antimony, arsenic, selenium and phosphorus impurities is intended to include those impurities in the free or elemental form as well as those impurities in any combined form.
"According to the method of this invention antimony, arsenic, selenium, phosphorus, and combinations of two or more thereof, whether in elemental or combined form, are removed from hydrocarbonaceous liquids that have been obtained by liquefying normally solid coal, liquefying normally solid oil shale, or liquefying normally solid-like tar sands. The hydrocarbonaceous liquid feed is contacted with at least one of the materials set forth hereinabove, the material being in a particulate form and preferably having a surface area of at least 1 square meter per gram, still more preferably at least 50 square meters per gram. The material can be employed by itself or in combination with a conventional support such as silica, alumina, magnesia, zirconia, thoria, zinc oxide, chromium oxide, naturally occurring supports such as clays, kieselguhr, Fuller's earth, pumice, bauxite, and the like, and combinations of two or more thereof whether naturally occurring or synthetically prepared.
"The material, whether supported or unsupported, can be in a particulate form to enhance intimate contacting of the material with the hydrocarbonaceous liquid to be treated. The particle size distribution is not critical although the greater the surface area the better from a point of view of completeness of contacting between the liquid and the material. Generally, the material can be in a form such that at least about 50 weight percent thereof has a largest cross-sectional dimension (i.e., the diameter of a particle if it is round or the longest dimension through the center of a particle if it is not round) of no longer than about 1/2 inch. The material can be in any physical form including powders, pellets, granules, spheres, flakes, cylinders, and the like. Any amount of the material can be employed on a support.
"Any amount of the material can be employed in the process of this invention, the more material that is present the better the removal of the impurity and the longer the material can be left in the process for treating new portions of liquid feed.
"As regards the oxides and sulfides of the metals set forth hereinabove, the ferric, nickelic, cobaltic, ferrous, nickelous, and cobaltous forms can be employed. For example, ferric oxides, both Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, nickelic oxides, Ni.sub.2 O.sub.3 and Ni.sub.3 O.sub.4, and cobaltic oxides, Co.sub.2 O.sub.3 and Co.sub.3 O.sub.4, can be employed. Similar reasoning is applicable to the comparable sulfides of the metals and to the ferrous, cobaltous, and nickelous forms of the oxides and sulfides.
"The liquid to be treated is mixed with the material, such as in a fixed bed reactor, at a temperature of at least 300.degree. F., preferably at least 700.degree. F., still more preferably from about 700.degree. to about 850.degree. F., under a reducing atmosphere, and for a time sufficient to achieve the desired degree of removal of impurity, generally at least about 1 minute. The reducing atmosphere is preferably provided by molecular hydrogen being present with the liquid as the liquid contacts the subdivided material. Preferably, there is a hydrogen partial pressure present of at least 500 psig, preferably at least 1500 psig."
Briefly summarized, the solid particulate material may comprise, for example, oxides or sulfides of iron, cobalt and nickel; alone or in combination with a supporting matrix, such as alumina. The solid particulate material may be employed in a plurality of processes or ways; for example, in a guard chamber to remove the arsenic from the fluid stream. Consequently, it is referred to herein, as a synonym and in shorthand nomenclature as "guard chamber material". After a sufficient amount of arsenic has been adsorbed, or removed from the stream, the material may contain 20-30 weight percent of the contaminant, such as arsenic, and is referred to as "spent". Disposal of the spent guard chamber material containing the poisonous contaminant presents a problem.
The literature suggests that roasting arsenic bearing ores in air will remove arsenic from the ores. Experience indicates, however, that only 40-60 percent, of the arsenic as measured by arsenic change in the guard bed material before and after roasting, is removed by roasting in air at temperatures below 2000.degree. F.
The prior art has not provided a totally satisfactory solution for disposing of the spent guard chamber material or of removing the contaminant, such as arsenic, therefrom such that both the arsenic and the spent guard chamber material can be employed in commercially useful processes. For example, the separated contaminant can be oxidized and disposed of as an article of commerce, or salable product. As is well known, the compounds of arsenic, as well as arsenic itself, have several commercially useful forms. For example, the arsenic may be employed with material, such as aluminum, gallium and indium to form III-V semi-conductor compounds. Such semi-conductor compounds are employed in forming terminal diodes, varactor diodes, transistors, solar cells, experimental lasers, and Hall-effect and infra-red devices. The largest market, however, is for the compounds or arsenic, such as the arsenates that are employed in agriculture for various insecticides, biocides and the like. Arsenic acid is being used increasingly as a defoliant for cotton. Also, arsanilic acid is used as a feed supplement for poultry and the like. The preparation of these compounds is described in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Anthony Standen Editor, Interscience Publishers, New York, New York, 1963, Vol. 2, pages 711-731; and that descriptive matter is embodied herein by reference for supplying the details of the steps of preparation of the respective element and compounds from arsenic, arsenic sulfide, arsenic trioxide and similar arsenic compounds such as may be produced in the method of this invention.
Similarly, the separated guard chamber material, sans the contaminant, can be recycled for subsequent use as active guard chamber material or can be disposed of as any other inert material if desired. Ordinarily, of course, it will be advantageous to regenerate and reuse the spent guard chamber material as will be described hereinafter.